Field
The present invention relates to a substrate recycling method, and more particularly, to a method of recycling a growth substrate separated from a nitride epitaxial layer.
Discussion of the Background
A technology of separating a substrate from an epitaxial layer after growing the substrate on the epitaxial layer is used in manufacture of light emitting devices. For example, a vertical type gallium nitride-based light emitting diode may be fabricated by growing epitaxial layers including n-type and p-type semiconductor layers on a growth substrate, followed by separating the growth substrate therefrom. Luminous efficacy of the light emitting diode can be improved by attaching a support substrate, which has higher thermal conductivity than the growth substrate, to the epitaxial layers.
In this way, the growth substrate is used for growth of the epitaxial layers and is then separated from the epitaxial layers after a separate support substrate different from the growth substrate is attached to the epitaxial layers in consideration of operating characteristics of the diode. The growth substrate may be separated from the epitaxial layers by, for example, laser lift-off, chemical lift-off, thermal or mechanical stress lift-off, and the like.
The separated growth substrate may be reused as a substrate for growing an epitaxial layer, thereby reducing substrate manufacturing costs.
In order to reuse the substrate separated from the epitaxial layer, the separated substrate is subjected to planarization using chemical mechanical polishing. However, since a substrate for growing a gallium nitride-based semiconductor layer or the gallium nitride-based semiconductor layer grown thereon has very high hardness, it may be difficult to achieve surface planarization through chemical mechanical polishing. As a result, the surface of the substrate subjected to chemical mechanical polishing includes many scratches and may suffer from cracking.
Moreover, when the gallium nitride-based semiconductor layer remains on an initial substrate used as the growth substrate, the remaining gallium nitride-based semiconductor layer may break when subjected to chemical mechanical polishing, thereby making selection of suitable process conditions difficult.
On the other hand, a technique of completely removing the gallium nitride-based semiconductor layer remaining on the substrate by heating to high temperature may be used. However, removal of the grown gallium nitride-based semiconductor layer through heating may incur high costs and cause damage to a growth substrate, for example, when the growth substrate is a gallium nitride substrate.